Relative importance of acid coating on ice nuclei in the deposition and contact modes for wintertime Arctic clouds and radiation

Abstract

Aerosols emitted from volcanic activities and polluted mid-latitudes regions are efficiently transported over the Arctic during winter by the large-scale atmospheric circulation. These aerosols are highly acidic. The acid coating on ice nuclei, which are present among these aerosols, alters their ability to nucleate ice crystals. In this research, the effect of acid coating on deposition and contact ice nuclei on the Arctic cloud and radiation is evaluated for January 2007 using a regional climate model. Results show that the suppression of contact freezing by acid coating on ice nuclei leads to small changes of the cloud microstructure and has no significant effect on the cloud radiative forcing (CRF) at the top of the atmosphere when compared with the effect of the alteration of deposition ice nucleation by acid coating on deposition ice nuclei. There is a negative feedback by which the suppression of contact freezing leads to an increase of the ice crystal nucleation rate by deposition ice nucleation. As a result, the suppression of contact freezing leads to an increase of the cloud ice crystal concentration. Changes in the cloud liquid and ice water contents remain small and the CRF is not significantly modified. The alteration of deposition ice nucleation by acid coating on ice nuclei is dominant over the alteration of contact freezing.

Anthropogenic Aerosol Influences on Mixed-Phase Clouds

“…If, however, the main effect of anthropogenic activity were a coating of INPs with acids (sulfuric acid, nitric acid), this would reduce their ice nucleating ability and result in fewer ice crystals that grow to larger sizes and sediment more readily without converting the whole MPC into an ice cloud [25]. Alternatively, ice may only form at colder temperatures.…”

“…MPCs may be stabilized due to anthropogenic activity due to the deactivation effect [25] such that the sulfate-induced inhibition of freezing leads to fewer and larger ice crystals both in MPCs and pure ice clouds [27]. Aerosol effects on Arctic MPCs have received lots of attention because MPCs play a central role in Arctic climate change and sea ice loss [41].…”

The relative impact of cloud condensation nuclei and ice nucleating particle concentrations on phase partitioning in Arctic mixed-phase stratocumulus clouds

“…In cases where INPs are transported over long distances and coated in sulfate or organic materials, an increased concentration of INPs may actually be linked to a "deactivation effect". This is because coated particles generally freeze at colder temperatures (Cziczo et al, 2009;Sullivan et al, 2010;Girard and Sokhandan, 2014), changing the number, size, and fall speeds of nucleated ice crystals and increasing cloud lifetime. The deactivation effect can cause a significant increase in surface warming, since a decrease in droplet size in optically thin clouds for constant LWP can produce a significant increase in cloud longwave emissivity (Garrett and Zhao, 2006).…”

The relative impact of cloud condensation nuclei and ice nucleating particle concentrations on phase-partitioning in Arctic Mixed-Phase Stratocumulus Clouds

“…In cases where INPs are transported over long distances and coated in sulfate or organic materials, an increased concentration of INPs may actually be linked to a "deactivation effect". This is because coated particles generally freeze at colder temperatures (Cziczo et al, 2009;Sullivan et al, 2010;Girard and Sokhandan, 2014), changing the number, size and fall speeds of nucleated ice crystals and increasing cloud lifetime. The deactivation effect can cause a significant increase in surface warming, since a decrease in droplet size in optically thin clouds for constant LWP can produce a significant increase in cloud longwave emissivity (Garrett and Zhao, 2006).…”